Sills in Sedimentary Basins and Petroleum Systems

Our knowledge of igneous emplacement in sedimentary basins has been revolutionised by studies of offshore 3D seismic reflection data, where large scale structures and relationships are realised. These offshore data sets require detailed information from onshore analogues to fully understand subsurface structure of such intrusions and their potential effect on petroleum systems. The Inner Hebrides of Western Scotland, which contains an onshore record of the extensive Palaeogene magmatic activity that affected much of the North Atlantic, allows us to examine some of the classic sill geometries on a seismic to sub-seismic (outcrop) scale. As hydrocarbon exploration moves to more challenging basins, it is clear the need exists for us to fully understand the role in which intrusive volcanism plays in active hydrocarbon systems. Intrusions in general can have major effects on prospective sedimentary basins by forming interconnected low-permeability zones which can compartmentalise significant volumes of source and reservoir rock. We present a series of outcrop case studies which allow the potential influences of sills on what would represent potential source and reservoir rock intervals to be addressed and discuss the wider implications for sill emplacement in such basins.